I agree that the novels are better than the films but I still love the films to death.
Jurassic Park still followed the basic story of the novel. They just took out the extra story elements to make the movie a smoother adventure film. It basicly took out parts in The book that made the story preachy.
I don't know what happened with TLW. I haven't gotten the blu-ray yet to watch the new making of features but I'm assuming the reason for changing the story that much is never really explained. I still like the film. The trailer going over the cliff is still one of my favorite scenes out of the whole series but I liked the story in the novel more. I would have prefered the Dodgson goes to the island story then InGen taking dinosaurs off the island.